Water-Cooled Oil-Free Air Compressor

ABSTRACT

A water-cooled oil-free air compressor which features compactness and ensures improved productivity and maintainability. The compressor is an oil-free screw compressor which includes a low pressure stage compressor body, an intercooler for water-cooling the compressed air discharged from the low pressure stage compressor body, a high pressure stage compressor body for further compressing the compressed air cooled by the intercooler, and an aftercooler for water-cooling the air discharged from the high pressure stage compressor body. The intercooler and aftercooler each have a plurality of units, all of which are almost equal in shape. A cooler header on each or either of the inlet and outlet sides for compressed air is shared by the units of each cooler.

BACKGROUND OF THE INVENTION

The present invention relates to water-cooled oil-free air compressors and more particularly to air compressors which use a cooling device for cooling the air compressed in multiple stages.

Most conventional two-stage oil-free screw compressors which have a low pressure stage compressor body and a high pressure stage compressor body use an intercooler for cooling the air compressed by the low pressure stage compressor body and an aftercooler for cooling the air compressed by the high pressure stage compressor body.

The compressors as described in JP-A No. H8-61271 and JP-A No. H11-22688 are known as water-cooled two-stage compressors having an intercooler and an aftercooler. In the compressor as described in JP-A No. H8-61271, cooling water is first to the aftercooler and then to the intercooler, and in the compressor as described in JP-A No. H11-22688, the cooling water path is branched into a cooling water path for cooling the intercooler and a cooling water path for cooling the aftercooler and after cooling the intercooler and aftercooler, the paths join together to discharge cooling water. These compressors have one intercooler and one aftercooler.

The compressors as described in JP-A No. 2002-130172 and JP-A 2006-249934 are known as compressors designed for compactness. In the compressor as described in JP-A No. 2002-130172, the intercooler and aftercooler are integral with each other and a cooling water inlet port is located on the aftercooler side and a cooling water outlet port is located on the intercooler side. JP-A 2006-249934 discloses that the compressor uses a plate type heat exchanger for a cooler with focus on heat exchanger size reduction.

SUMMARY OF THE INVENTION

In recent years, with growing demand for compressed air, there has been a trend toward large size compressors that provide high output and deal with large volumes of air. As compressors provide higher output and deal with larger volumes of air, the coolers used therein tend to be larger in size.

If a compressors uses one intercooler and one aftercooler like those as described in JP-A No. H8-61271 and JP-A No. H11-22688 and is large in size, its intercooler and aftercooler must be large. In such a compressor, the space occupied by the coolers and cooler inlet and outlet pipes in the compressor package must be large, which is an impediment to compressor size reduction. More specifically, when a large compressor deals with a large volume of air, the intercooler and aftercooler shell diameter and length must be large enough to secure the required cooling capacity. This means that the cooler volume must be large and it is difficult to reduce the overall compressor size.

Furthermore, since the intercooler and aftercooler lie in the compressed air discharge route, there is high pressure air in the air paths inside the coolers. A large compressor which deals with a large volume of air has a problem that the cooler volume must be large enough as mentioned above, and if a cooler breakdown occurs, its influence will be serious. Another problem is that as the cooler size is larger, the cooler maneuverability and working efficiency in maintenance including cleaning deteriorate.

In the compressor as described in JP-A No. 2002-130172, the intercooler and aftercooler are integral with each other so that a certain degree of cooler compactness can be achieved. However, the intercooler and aftercooler are located opposite to each other, which constitutes a restriction on the arrangement of the coolers. Therefore, when the cooler size is increased in order to achieve higher putout (larger air volume) of the air compressor, it may be difficult to reduce the overall compressor size because the coolers are integral with each other.

Although the compressor as described in JP-A 2006-249934 is designed for cooler compactness, it also offers no solution to the problem that the cooler size must be increased to cope with higher compressor output (larger air volume). Therefore, a solution to the problem has been anticipated.

The present invention has been made in view of the above circumstances and has an object to provide an air compressor which features compressor package compactness and ensures improved productivity and maintainability.

In order to achieve the above object, according to one aspect of the present invention, there is provided a water-cooled oil-free air compressor which includes a low pressure stage compressor body, an intercooler for water-cooling compressed air discharged from the low pressure stage compressor body, a high pressure stage compressor body for further compressing the compressed air cooled by the intercooler, and an aftercooler for water-cooling air discharged from the high pressure stage compressor body.

The compressor has the following features:

-   -   The intercooler includes a plurality of intercooler units;     -   The aftercooler includes a plurality of aftercooler units;     -   The intercooler units each have a cooling water inlet and a         cooling water outlet;     -   The aftercooler units each have a cooling water inlet and a         cooling water outlet; and     -   A first cooling water path is provided to supply cooling water         first to one aftercooler unit, then to one intercooler unit and         a second cooling water path is provided to supply cooling water         first to another aftercooler unit, then to another intercooler         unit.

Preferably the above compressor is characterized as follows:

-   (a) The first cooling water path and the second cooling water path     are symmetrical to each other in shape. -   (b) The intercooler and the aftercooler each have a cooler header     covering a compressed air inlet side and a cooler header covering a     compressed air outlet side and a cooler header on either or each of     the compressed air inlet side and outlet side of the intercooler or     the aftercooler is shared by the intercooler units or the     aftercooler units. -   (c) Upstream of the aftercooler, a discharge pipe for compressed air     flowing into the aftercooler is branched into a plurality of pipes     leading to the aftercooler units and a check valve is provided in     each branch discharge pipe. -   (d) The intercooler units and the aftercooler units have the same     shape.

More preferably, the intercooler and the aftercooler are arranged so as to make a flow direction of compressed air flowing in the intercooler and a flow direction of compressed air flowing in the aftercooler opposite to each other, a flow direction of compressed air flowing in the intercooler and a flow direction of cooling water flowing in the intercooler are opposite to each other and a flow direction of compressed air flowing in the aftercooler and a flow direction of cooling water flowing in the aftercooler are opposite to each other, and a cooling water pipe for connecting a cooling water outlet of one aftercooler unit and a cooling water inlet of one intercooler unit and a cooling water pipe for connecting a cooling water outlet of another aftercooler unit and a cooling water inlet of another intercooler unit are provided.

In the above compressor, it is preferable that the cooling water pipe for connecting the cooling water outlet of one aftercooler unit and the cooling water inlet of one intercooler unit and the cooling water pipe for connecting a cooling water outlet of another aftercooler unit and the cooling water inlet of another intercooler unit be arranged symmetrically.

Furthermore, if the compressor includes a motor for driving the low pressure stage compressor body and the high pressure stage compressor body, a plurality of gears for transmitting power of the motor to the low pressure stage compressor body and the high pressure stage compressor body, a gear casing for housing the gears, and a cooler rack located opposite to the gear casing with respect to the motor to hold the intercooler and the aftercooler in a higher position than the motor, it is preferable that the positional relation be as follows:

-   (a) The low pressure stage compressor body and the high pressure     stage compressor body are placed side by side, protruding over the     motor from the gear casing. -   (b) The low pressure stage compressor body is located on a     compressed air inlet side of the intercooler and the high pressure     stage compressor body is located on a compressed air inlet side of     the aftercooler to make the flow direction of compressed air flowing     in the intercooler and the flow direction of compressed air flowing     in the aftercooler opposite to each other.

In the above case, on the cooler rack, the aftercooler is placed above the intercooler.

According to the present invention, coolers can be simplified and it is possible to provide a water-cooled two-stage oil-free air compressor which features compactness and ensures improved productivity and maintainability.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a schematic diagram showing a water-cooled two-stage oil-free screw compressor according to an embodiment of the present invention;

FIG. 2 shows the configuration of the water-cooled two-stage oil-free screw compressor;

FIG. 3 shows the configuration of a cooling system; and

FIG. 4 is a sectional view of a cooler unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 and FIG. 2, a preferred embodiment of the present invention assumes a multistage air compressor which includes: a low pressure stage compressor body 1; an intercooler 3 for water-cooling the compressed air discharged from the low pressure stage compressor body 1; a high pressure stage compressor body 2 for further compressing the compressed air cooled by the intercooler 3; and an aftercooler 4 for water-cooling the air discharged from the high pressure stage compressor body 2. According to this embodiment, the air compressor is characterized by adopting a so-called one-pass system in which two intercooler units and two aftercooler units are provided to ensure compactness of the intercooler 3 and the aftercooler 4.

This embodiment offers the following four advantageous effects, which will be explained in detail later.

First, as compared with the conventional techniques (for example, those described in JP-A No. H8-61271 and JP-A No. H11-22688 in which one cooler head is provided on each of the inlet and outlet sides of an intercooler and an aftercooler, this embodiment is advantageous in the following point.

In the conventional techniques, which use one intercooler and one aftercooler, when the compressor is large and provides high output with a large volume of air, the intercooler and aftercooler must be large as well. As a consequence, working efficiency in maintenance including cleaning the cooler inside deteriorates and the space occupied by the coolers and cooler inlet and outlet pipes in the compressor package is large, constituting a bottleneck in the effort to reduce the compressor size.

By contrast, in this embodiment, the intercooler 3 and aftercooler 4 each include two units so that maintainability of the coolers 3 and 4 is improved and the compressor package can be compact. In addition, even if a cooler breakdown occurs, leakage of compressed air is reduced due to the compactness of the cooler units.

Second, concerning check valves provided in the compressed air paths, this embodiment is advantageous as follows. In the conventional techniques which use one intercooler and one aftercooler (for example, those described in JP-A No. H8-61271 and JP-A No. H11-22688), one check valve is provided for one compressor as suggested in JP-A No. 2002-130172. In this case, as the compressor provides higher output and deals with a larger volume of air, the check valve size must be larger. If that is the case, the check valve cost is higher and it is less easy to simplify the check valve installation structure and improve maintainability.

In this embodiment, a plurality of cooler units are used and the path for compressed air flowing into the coolers is branched off so that two check valves can be provided. As shown in FIG. 1, two check valves 13 are installed at the inlets of the two aftercooler units 4 a and 4 b respectively so that the check valves 13 are small, the compressor package is compact and the installation structure of the check valves 13 is simplified and maintainability is improved. In addition, for further improvement in productivity and maintainability, the check valves 13 are so located that they can be easily accessed from outside.

Third, concerning the compressed air paths, the embodiment is also advantageous as follows. In this embodiment, compressed air flows into plural cooler units, which means that the air path is branched off. In this case, if one cooler head is provided at each of the inlets and outlets of the coolers, not a few pipes will be required for the inlets and outlets. In this embodiment, instead a common header is provided at each or either of the inlet and outlet in the two intercooler units 3 a and 3 b and the two aftercooler units 4 a and 4 b to decrease the number of cooler inlet and outlet pipes for simplicity.

Fourth, since one cooler 3 (4) includes plural cooler units, in this case 3 a and 3 b (4 a and 4 b), productivity and maintainability can be improved. In the conventional techniques, the intercooler and aftercooler are different in size and shape (JP-A No. H8-61271 and JP-A No. H11-22688) or integral with each other (JP-A No. 2002-130172 and JP-A No. 2006-249934), so when assembling the compressor or cleaning or replacing a cooler, it is necessary to prepare different parts for the intercooler and aftercooler. On the other hand, in this embodiment, the intercooler units and aftercooler units are all common and their parts are interchangeable, leading to improvement in productivity and maintainability.

When the intercooler 3 and aftercooler 4 have more than one unit, for example, two units 3 a, 3 b, 4 a and 4 b, the two intercooler units 3 a and 3 b or the two aftercooler units 4 a and 4 b must be equal in cooling capacity. Therefore, in this embodiment, cooling water pipes are disposed in parallel and symmetrically for the intercooler 3 and aftercooler 4 which constitute two cooler sets, each set consisting of an intercooler unit and an aftercooler unit, so that equal amounts of cooling water flow into the two intercooler units 3 a and 3 b and the two aftercooler units 4 a and 4 b, and the intercooler units (aftercooler units) are equal in cooling capacity.

Although the units of the intercooler 3 and aftercooler 4 are common in this embodiment, for the sake of drain reduction the intercooler 3 must be lower in cooling capacity than the aftercooler 4. In this embodiment, the cooling water flow system is specially designed to address this need. More specifically, it is designed so that the aftercooler 4 is first cooled and the intercooler 3 is cooled by the cooling water used for the aftercooler 4, which has a temperature higher than before. The cooling capacity of the intercooler 3 and that of the aftercooler 4 are thus controlled.

Alternatively, the cooling capacity can be controlled by making the number of cooler units of the intercooler 3 and that of the aftercooler 4 different (for example, three aftercooler units and two intercooler units are used). This means that common parts can be used and the cooling capacity can be easily controlled, contributing to improvement in productivity.

For the purpose of improvement in the cooling capacity of a cooler, it is effective that the inlet and outlet ports for compressed air as a hot fluid are opposite to those for cooling water as a cool fluid and their flow directions are opposite or they flow as counterflows. For both the intercooler 3 and aftercooler 4, it is desirable that cooling water be made to flow first for higher temperature compressed air. Therefore, the aftercooler 4 and intercooler 3 are arranged in parallel as mentioned above and since cooling water is to be supplied first to the aftercooler 4 and then to the intercooler 3, the outlet for cooling water from the aftercooler 4 is located near the inlet for cooling water into the intercooler 3 in order to shorten the cooling water pipe and simplify the piping. In other words, the piping is arranged so that the flow direction of compressed air in the aftercooler 4 is opposite to that in the intercooler 3 (at the same time, the flow directions of cooling water in the coolers are also opposite to each other), so the cooling water pipe is shortened, the structure is simplified and productivity is improved.

As described above, according to this embodiment, space for the coolers 3 and 4 in the compressor unit is saved and the compressor can be more compact. In addition, since the piping is simplified and the cooler size is decreased, productivity and maintainability can be improved.

FIRST EMBODIMENT

The first embodiment of the present invention will be described in detail referring to the accompanying drawings. The description will be given below by taking as an example a screw compressor which compresses air by rotation of male and female rotors.

FIG. 1 is a schematic diagram showing a water-cooled two-stage oil-free screw compressor 30 having a low pressure stage compressor body 1 and a high pressure stage compressor body 2. The low pressure stage compressor body 1 and high pressure stage compressor body 2 each include a pair of rotors, i.e. a male rotor and a female rotor. The compressor according to this embodiment is a screw air compressor which compresses air by rotation of the male and female rotors.

Pinion gears 21 are fitted to the axial ends of the male rotors of the low pressure stage compressor body 1 and high pressure stage compressor body 2. These pinion gears 21 are engaged with a bull gear 23 fitted to one end of a driving shaft inside a gear casing 28 so that motor power is transmitted to the low pressure stage compressor body 1 and high pressure stage compressor body 2. Although FIG. 1 shows that the bull gear 23 is located on the output shaft of a motor 26 and engaged with the pinion gears 21 at the axial ends of the male rotors, instead an intermediate shaft may be located between the motor output shaft and the male rotors. If an intermediate shaft is provided, the power of the motor 26 is transmitted to the low pressure stage compressor body 1 and high pressure stage compressor body 2 through the intermediate shaft.

Next, the structure of the water-cooled two-stage oil-free screw compressor according to this embodiment will be explained, paying attention to flows of air compressed by the compressor.

An intake throttle valve 12 which regulates the flow rate of air taken into the low pressure stage compressor body 1 is located on the intake side of the low pressure stage compressor body 1. The air, from which foreign matter is removed by a filter (not shown), is passed through the intake throttle valve 12 and introduced into the low pressure stage compressor body 1 and compressed to a prescribed pressure level and discharged through the outlet of the low pressure stage compressor body 1. The compressed air discharged from the low pressure stage compressor body 1 is led into an intermediate discharge pipe A.

The air compressed by the low pressure stage compressor body 1 and led into the intermediate discharge pipe A is cooled by the intercooler 3. In this embodiment, the intermediate discharge pipe A is branched into plural pipes upstream of the cooler headers 6 which serve as holes to introduce air into the intercooler 3.

As shown in FIG. 1, the discharge pipe A is bifurcated at the inlets of the cooler headers 6 and the two flows of compressed air are introduced in parallel into the two intercooler units 3 a and 3 b located in the air path between the low pressure stage compressor body 1 and high pressure stage compressor body 2 to be cooled there. The two flows of compressed air cooled by the intercooler 3, comprised of two intercooler units, join together at a cooler header 7 attached to the outlet side of the intercooler 3 before being led into an intermediate discharge pipe B.

The compressed air cooled by the intercooler 3 and led into the intermediate discharge pipe B is taken into the high pressure stage compressor body 2 located downstream thereof. The compressed air further compressed by the high pressure stage compressor body 2 is discharged from the high pressure stage compressor body 2 and led into a high pressure stage discharge pipe C. The discharge pipe C, which connects the high pressure stage compressor body 2 and the aftercooler 4, is branched into plural pipes upstream of cooler headers 8 of the aftercooler 4. A check valve 13 is installed in each flow path downstream of the branching point of the discharge pipe C, in which the check valves 13 are located upstream of the aftercooler headers 8.

Therefore, as shown in FIG. 1, the compressed air discharged into the high pressure stage discharge pipe C is divided into two flows at a point midway in the discharge pipe C and the flows of compressed air pass through the two check valves 13 located downstream thereof before being taken in parallel into the aftercooler 4, comprised of two aftercooler units 4 a and 4 b, and being cooled there. The flows of compressed air cooled by the aftercooler 4 join together in a cooler header 9 attached to the outlet side of the aftercooler 4 before being exhausted through a compressed air outlet port.

It should be noted that whereas one cooler header 6 is attached to the inlet side of each of the intercooler units 3 a and 3 b of the intercooler 3 and one cooler header 8 is attached to the inlet side of each of the aftercooler units 4 a and 4 b of the aftercooler 4, only one cooler header is attached to the outlet sides of the two intercooler units 3 a and 3 b and also only one cooler header is attached to the outlet sides of the two aftercooler units 4 a and 4 b so that the two flows of compressed air join together at each outlet side, and the flows of compressed air join together in the outlet side.

Next, the structure of the water-cooled two-stage oil-free screw compressor according to this embodiment will be explained, paying attention to the compressor cooling mechanism.

In an oil-free screw compressor, since there is no cooling means in the process of compressing air as working gas, the high pressure stage compressor body 2 and the low pressure stage compressor body 1 generate heat due to compression heat. The compressed air has a high temperature and is too hot for a consumer to use. In addition, by cooling the gas compressed by the low pressure stage compressor body 1 and supplying it to the high pressure stage compressor body 2, the overall efficiency of the oil-free screw compressor 30 is improved. For the above reasons, cooling water is supplied to various parts of the oil-free compressor 30. The cooling water is routed as follows.

The path for cooling water cooled by a cooling tower (not shown) is branched at the cooling water inlet port into a cooling water path for the aftercooler 4 and intercooler 3 and a cooling water path for the oil cooler 10, blower cooler 11, high pressure stage compressor body 2, and low pressure stage compressor body 1. The cooling water path for the aftercooler 4 and intercooler 3 first leads to the aftercooler 4 to cool the air discharged from the high pressure stage compressor body 2, then reaches the intercooler 3 to cool the air discharged from the low pressure stage compressor body 1 before returning the cooling water to the cooling tower or the like through a cooling water outlet port. In the intercooler 3 and aftercooler 4, the flow direction of cooling water is opposite to the flow direction of compressed air to make it a counterflow and in both the intercooler 3 and aftercooler 4, cooling water is supplied from the bottom of the shell and drained from its top.

In this embodiment, the intercooler 3 and aftercooler 4 each have two units (intercooler units 3 a and 3 b and aftercooler units 4 a and 4 b) and the cooling water pipe in the path for cooling them is bifurcated at the inlet of the aftercooler 4 into a pipe for cooling one cooler set, i.e. the aftercooler unit 4 a and intercooler unit 3 a and a pipe for cooling the other cooler set, i.e. the aftercooler unit 4 b and intercooler unit 3 b. After leaving the intercooler 3, the two cooling water pipes join together and lead to a cooling water outlet port. (Hereinafter, they may be called the “first cooling water path” and “second cooling water path” respectively.)

On the other hand, cooling water in the path for cooling the oil cooler 10, blower cooler 11, high pressure stage compressor body 2 and low pressure stage compressor body 1 is first led to the oil cooler 10 to cool lubricating oil, then led to the blower cooler 11 to cool the air released during no-load operation. Next, the cooling water is led to a cooling jacket provided on the casing of the high pressure stage compressor body 2 to cool the high pressure stage compressor body 2, then led to a cooling jacket provided on the casing of the low pressure stage compressor body 1 to cool the low pressure stage compressor body 1 before returning to the cooling tower through the cooling water outlet port.

A valve is attached to the inlet of the cooling water path for the oil cooler 10. In this embodiment, since the cooling water pipe from the cooling water inlet port is bifurcated into a pipe for the cooling water path for compressed air and a pipe for the cooling water path for oil and the compressor bodies, a valve is used to regulate the cooling water ratio between the path for the aftercooler 4 and intercooler 3 and the path for the oil cooler 10, blower cooler 11 and high pressure stage compressor body 2, and low pressure stage compressor body 1.

The lubricating oil cooled by the oil cooler 10 lubricates the bearings and pinion gears of the low pressure stage compressor body 1 and high pressure stage compressor body 2, the timing gears and the bearings of the intermediate shaft in the gear casing 28, the pinion gears and bull gear fitted to the intermediate shaft and the bull gear fitted to the rotation shaft of the motor and so on before being stored in an oil reservoir at the bottom of the gear casing 28. Then, the oil is led by an oil pump into the oil cooler 10 and cooled by cooling water. The lubricating oil circulates in this way.

In this embodiment, the compressed air path is branched into two paths upstream of the intercooler 3 and after the compressed air is cooled by the intercooler 3, the paths join together. After air is further compressed by the high pressure stage compressor body 2, the compressed air path is branched upstream of the aftercooler 4. The paths join together after the compressed air is cooled by the aftercooler 4 to supply the compressed air to the outside. On the other hand, the cooling water path is branched into a first cooling water path and a second cooling water path which are independent of each other. More specifically, after the path is branched into two paths before supplying cooling water to the aftercooler 4, the flows of cooling water in the two paths cool the aftercooler 4 and then go to the intercooler 3 respectively without joining together. Therefore, it is desirable to supply an equal amount of cooling water to both the paths to ensure uniformity in cooling performance. Therefore, it is desirable that the first cooling water path and cooling water path be the same or mutually symmetrical in terms of shape.

Next, the internal arrangement of the air compressor package according to this embodiment will be described referring to FIG. 2. FIG. 2 shows the configuration of the water-cooled two-stage oil-free screw compressor, in which parts other than substantial ones are omitted.

As shown in FIG. 2, a pedestal on which the motor 26 and gear casing 28 are mounted is placed on the base and adjacent to the pedestal is a cooler rack 18 on which the coolers 3 and 4 are mounted. Power from the motor 26 is transmitted through various gears in the gear casing 28 to the low pressure stage compressor body 1 and high pressure stage compressor body 2. In this embodiment, as shown in the figure, the gear casing 28 is located on the output shaft side of the motor 26 and the low pressure stage compressor body 1 and high pressure stage compressor body 2 are placed side by side in a way to protrude over the motor 26 from above the gear casing 28. In other words, both the compressor bodies 1 and 2 lie over the motor 26.

The cooler rack 18 is located opposite to the gear casing 28 (front left in the figure) with respect to the motor 26. The cooler rack 18 has legs and the cooler rest is in a higher position than the motor 26. This arrangement facilitates heat radiation of the motor 26 because the space on the side of the motor 26 which is opposite to the gear casing 28 is open.

The intercooler 3 and aftercooler 4 are placed on the cooler rest of the cooler rack 18. As mentioned above, the low pressure stage compressor body 1 lies over the motor 26 and compressed air discharged from the low pressure stage compressor body 1 flows into the discharge pipe A and enters the intercooler 3. Since the distance between the low pressure stage compressor body 1 and intercooler 3 is short, the air path can be short and the intermediate discharge pipe A can be simplified.

The intercooler 3 in this embodiment is explained below. As shown in FIG. 2, the intercooler 3 is mounted on the cooler rack 18. The intercooler 3 includes two intercooler units 3 a and 3 b which are placed on the cooler rack 18 side by side by cooler supporting members. The two units of the aftercooler 4 are placed side by side like the intercooler 3, over the intercooler 3. Since the aftercooler 4 lies over the intercooler 3, the check valves 13 can be accessed easily and installed easily, contributing to easy maintenance.

The cooler headers 6 and 7 are attached to the compressed air inlet and outlet sides of the two intercooler units 3 a and 3 b of the intercooler 3 which are located side by side. In this embodiment, the discharge pipe A is branched upstream of the cooler headers 6 so that compressed air flows through two air paths into the intercooler units 3 a and 3 b where it is cooled.

The flows of compressed air cooled by the intercooler units 3 a and 3 b enter the cooler header 7 at the outlet side. The cooler header 7 in this embodiment has a structure which allows the flows of compressed air from the units to meet and the combined compressed air flow in the cooler header 7 goes through the discharge pipe B into the high pressure stage compressor body 2.

As shown in FIG. 2, both the compressor bodies 1 and 2, protruding over the motor 26 from the top of the gear casing 28, are arranged so as to simplify the piping. More specifically, the low pressure stage compressor body 1 is on the same side as the inlet of the intercooler 3 (front in the figure) and the high pressure stage compressor body 2 is on the same side as the outlet of the intercooler 3 (back in the figure). The discharge pipe B as the path for the air cooled by the intercooler 3 is also simplified.

The compressed air further compressed by the high pressure stage compressor body 2 is discharged into the high pressure stage discharge pipe C. The discharge pipe C extends upward and, on the downstream, extends toward the aftercooler 4.

Like the intercooler 3, the aftercooler 4 is comprised of two aftercooler units 4 a and 4 b like the intercooler 3, and has cooler headers 8 and 9 on the compressed air inlet and outlet sides respectively. As shown in the figure, the discharge pipe C is branched upstream of the cooler headers 8 and each branch pipe has a check valve 13. Each of these branch pipes is connected with the cooler header 8 provided on each of the cooler units 4 a and 4 b.

Therefore, compressed air, after being branched through the discharge pipe C, passes through the check valve 13 in each branch pipe and is introduced into the cooler header 8. The compressed air flowing from the cooler header 8 into the aftercooler 4 is cooled by the aftercooler 4 before joining the other flow of compressed air in the cooler header 9 on the outlet side and flowing out of the compressor package. The flow direction of compressed air in the intercooler 3 is opposite to that in the aftercooler 4 so that the discharge pipe is simplified due to the positional relation with the compressor bodies 1 and 2.

Next, the cooling water paths in this embodiment will be briefly described. As mentioned above, in this embodiment, the cooling water pipe for the path for cooling the intercooler units 3 a and 3 b and aftercooler units 4 a and 4 b is branched before the inlet of the aftercooler 4 into a pipe for cooling one set of cooler units, the aftercooler unit 4 a and intercooler unit 3 a, and a pipe for cooling the other set, the aftercooler unit 4 b and intercooler unit 3 b. This means that the flows of cooling water branched before being cooled by the coolers do not join together until they are cooled.

As mentioned above, the cooling water in the coolers flows in a direction opposite to the flow of compressed air to make a counterflow, so the flow direction of cooling water in the intercooler 3 is opposite to that in the aftercooler 4. Therefore, the cooling water pipe through which the cooling water used to cool the compressed air in the aftercooler 4 flows into the intercooler 3 can be shortened to simplify the structure. More specifically, the cooling water outlet of the aftercooler 4 as designated by reference numeral 17 in FIG. 2 and the cooling water inlet of the intercooler 3 as designated by reference numeral 16 can be close to each other, largely contributing to compactness from the viewpoint of the cooling water path.

Next, the structures of the intercooler 3 and aftercooler 4 will be described in detail. As mentioned above, the intercooler 3 and aftercooler 4 in this embodiment each use two cooler units. The structure of the coolers is shown in FIGS. 3 and 4. FIG. 3 shows the configuration of the cooling system which includes the intercooler 3 and aftercooler 4 and FIG. 4 is a sectional view of a cooler. For both the intercooler 3 and aftercooler 4, the shell 5 which forms the outside of the cooling part has the same dimensions.

As shown in FIG. 3, the intercooler 3 and aftercooler 4 each have two cooler units placed side by side on the cooler rack 18 in which the aftercooler 4 is in the upper position and the intercooler 3 is in the lower position. The cooler units are fixed on the cooler rest of the cooler rack 18 by supporting members. They are thus arranged with the required spacing between cooler units (between the cooler units 3 a and 3 b and between the cooler units 4 a and 4 b) and the required spacing between the coolers (between the intercooler 3 and aftercooler 4).

The inlets and outlets of the aftercooler 4 and intercooler 3 for air and cooling water are oriented in opposite directions to make counterflows as mentioned above. In the example of FIG. 3, cooling water is supplied into the cooler shell (explained later) from the cooling water inlet 16 (upper right in the figure) of the aftercooler 4 to cool high-pressure compressed air and then discharged through the outlet 17 (upper left in the figure). After that, it is supplied through the cooling water inlet 16 (lower left in the figure) into the intercooler 3 to cool middle-pressure compressed air and then discharged through the cooling water outlet 17 (lower right in the figure).

This configuration makes it possible that all cooler components including the cooling water paths are arranged in a compressor unit in a compact manner. In addition, by removing the pipes connected to the coolers and the bolts on the cooler rack 18, the entire coolers including the check valves 13 can be removed from the compressor unit. Furthermore, since all the cooler parts are common to the coolers, cooler maintenance including cleaning and replacement is easy.

Details of the inside of each unit of the intercooler 3 and aftercooler 4 are shown in FIG. 4. The intercooler 3 and aftercooler 4 adopt a so-called one-pass shell and tube heat exchanger. Here, “one-pass” means that the inlet and outlet for compressed air are in different positions and there is no reciprocating path. More specifically, air which flows in from one side is discharged at the other side and cooling water which flows in from the side where air is discharged is discharged at the side where air flows in.

The plurality of heat transfer tubes 14 installed inside the intercooler 3 and aftercooler 4 are all the same in terms of shape and the number of such tubes is almost equal for the coolers, and the heat transfer tubes 14 are disposed at regular intervals in the cooler shell 5. In order to hold these heat transfer tubes 14 stably inside the cooler shell 5 and form a cooling water path, pipe plates 15 are disposed in a staggered pattern at a plurality of points in the cooler unit axial direction.

The above explanation of the embodiment of the present invention assumes that the intercooler and aftercooler each use two units. However, the invention is not limited thereto and three or more intercooler and/or aftercooler units may be used without departing from the scope of the invention.

Although the above embodiment concerns a two-stage compressor, the same configuration can be applied to a multistage compressor which has three or more pressure stages and even in that case, the same advantageous effects can be achieved.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 

1. A water-cooled oil-free air compressor comprising: a low pressure stage compressor body; an intercooler for water-cooling compressed air discharged from the low pressure stage compressor body; a high pressure stage compressor body for further compressing the compressed air cooled by the intercooler; and an aftercooler for water-cooling air discharged from the high pressure stage compressor body, wherein the intercooler includes a plurality of intercooler units; wherein the aftercooler includes a plurality of aftercooler units; wherein the intercooler units each have a cooling water inlet and a cooling water outlet; wherein the aftercooler units each have a cooling water inlet and a cooling water outlet; and wherein a first cooling water path is provided to supply cooling water first to one aftercooler unit, then to one intercooler unit and a second cooling water path is provided to supply cooling water first to another aftercooler unit, then to another intercooler unit.
 2. The water-cooled oil-free air compressor according to claim 1, wherein the first cooling water path and the second cooling water path are symmetrical to each other in shape.
 3. The water-cooled oil-free air compressor according to claim 1, wherein the intercooler and the aftercooler each have a cooler header covering a compressed air inlet side and a cooler header covering a compressed air outlet side; and wherein a cooler header on either or each of the compressed air inlet side and outlet side of the intercooler or the aftercooler is shared by the intercooler units or the aftercooler units.
 4. The water-cooled oil-free air compressor according to claim 1, wherein upstream of the aftercooler, a discharge pipe for compressed air flowing into the aftercooler is branched into a plurality of pipes leading to the aftercooler units; and wherein a check valve is provided in each branch discharge pipe.
 5. The water-cooled oil-free air compressor according to claim 1, wherein the intercooler units and the aftercooler units have the same shape.
 6. The water-cooled oil-free air compressor according to claim 1, wherein the intercooler and the aftercooler are arranged so as to make a flow direction of compressed air flowing in the intercooler and a flow direction of compressed air flowing in the aftercooler opposite to each other; wherein a flow direction of compressed air flowing in the intercooler and a flow direction of cooling water flowing in the intercooler are opposite to each other and a flow direction of compressed air flowing in the aftercooler and a flow direction of cooling water flowing in the aftercooler are opposite to each other; and wherein a cooling water pipe for connecting a cooling water outlet of one of the aftercooler units and a cooling water inlet of one of the intercooler units and a cooling water pipe for connecting a cooling water outlet of another of the aftercooler units and a cooling water inlet of another of the intercooler units are provided.
 7. The water-cooled oil-free air compressor according to claim 6, wherein the cooling water pipe for connecting the cooling water outlet of the one aftercooler unit and the cooling water inlet of the one intercooler unit and the cooling water pipe for connecting the cooling water outlet of the another aftercooler unit and the cooling water inlet of the another intercooler unit are arranged symmetrically.
 8. The water-cooled oil-free air compressor according to claim 6, further comprising: a motor for driving the low pressure stage compressor body and the high pressure stage compressor body; a plurality of gears for transmitting power of the motor to the low pressure stage compressor body and the high pressure stage compressor body; a gear casing for housing the gears; and a cooler rack located opposite to the gear casing with respect to the motor to hold the intercooler and the aftercooler in a higher position than the motor, wherein the low pressure stage compressor body and the high pressure stage compressor body are placed side by side, protruding over the motor from the gear casing; and wherein the low pressure stage compressor body is located on a compressed air inlet side of the intercooler and the high pressure stage compressor body is located on a compressed air inlet side of the aftercooler to make the flow direction of compressed air flowing in the intercooler and the flow direction of compressed air flowing in the aftercooler opposite to each other.
 9. The water-cooled oil-free air compressor according to claim 7, further comprising: a motor for driving the low pressure stage compressor body and the high pressure stage compressor body; a plurality of gears for transmitting power of the motor to the low pressure stage compressor body and the high pressure stage compressor body; a gear casing for housing the gears; and a cooler rack located opposite to the gear casing with respect to the motor to hold the intercooler and the aftercooler in a higher position than the motor, wherein the low pressure stage compressor body and the high pressure stage compressor body are placed side by side, protruding over the motor from the gear casing; and wherein the low pressure stage compressor body is located on a compressed air inlet side of the intercooler and the high pressure stage compressor body is located on a compressed air inlet side of the aftercooler to make the flow direction of compressed air in the intercooler and the flow direction of compressed air flowing in the aftercooler opposite to each other.
 10. The water-cooled oil-free air compressor according to claim 8, wherein on the cooler rack, the aftercooler is placed above the intercooler.
 11. The water-cooled oil-free air compressor according to claim 9, wherein on the cooler rack, the aftercooler is placed above the intercooler. 